Method for hydrostatic extrusion of tubes

ABSTRACT

A press for hydrostatic extrusion of tubes includes a high pressure cylinder axially displaceable in a press stand with a die insertable into the cylinder and a pressure generating punch insertable into the cylinder to generate the pressure for extrusion. A mandrel is carried by a rod which passes through the pressure-generating punch. A hollow billet is inserted into such a structure which has the central opening therethrough at the point adjacent the die of smaller cross-section than that of the mandrel. When the mandrel is advanced towards the die, it engages the narrowed portion of the bore of the billet and presses it against the die, holding it there while the pressure chamber is advanced around the billet and the extrusion takes place.

mted States Patent 1 [111 336,662 Nilsson Feb. 5, 1974 [54] METHOD FOR HYDROSTATIC'EXTRUSION 3,751,958 8/1973 Nilsson 72/60 0F TUBES [75] Inventor: Jan Nilsson, Robertsfors, Sweden Primary Examiner Rjchard Herb [73] Assignee: Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden [57] ABSTRACT [22] Filed: June 5, 1973 A press for hydrostatic extrusion of tubes includes a high pressure cylinder axially displaceable in a press PP 0.: 367,104 stand with a die insertable into the cylinder and a pressure generating punch insertable into the cylinder [30] Foreign Application priority Data to generate the pressure for extrusion. A mandrel is June 12 1972 Sweden 7689/72 carried by a rod which passes through the pressuregenerating punch. A hollow billet is inserted into such a structure which has the central opening there- (g1. 724?;22322/(6): through at the point adjacent the die of Smaller cross 58] Fie'ld 269 272 section than that of the mandrel. When the mandrel is advanced towards the die, it engages the narrowed portion of the bore of the billet and presses it against [56] References Cited the die, holding it there while the pressure chamber is v UNITED STATES PATENTS advanced around the billet and the extrusion takes 3,397,562 8/l968 Fuchs, Jr. 72/54 place, 3,451,240 6/1969 Sauve 72/60 3,751,957 8/1973 Nilsson 72/60 1 Claim, 5 Drawing Figures PATENTE FEB 51974 SHEET 1 BF 2.

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METHOD FOR HYDROSTATIC EXTRUSION OF TUBES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for hydrostatic extrusion of tubes.

2. The Prior Art I For hydrostatic extrusion a billet is inserted in a pressure chamber formed by a high-pressure cylinder, a die with an opening having the cross-section desired in the product manufactured, and a pressure-generating punch which, when inserted into the cylinder, generates the pressure necessary for the extrusion process in a pressure medium surrounding the billet, thus influencing this from all sides. For extruding tubes a mandrel is required to shape the hollow in the tube. Equipment now in use for extruding tubes is shown and more fully described in US. Pat. application of Jan Nilsson et al. No. 145,184, filed May 20, 1971, now US. Pat. No. 3,751,958. In this extrusion equipment the forces exerted on the mandrel are taken up entirely inside the pressure chamber and transmitted to the die by a spacer tube. The pressure exerted on the inner end surface of the mandrel and which must be taken up by the spacer tube is extremely high and the wall of the spacer tube must therefore be strong. The pressure is F 1rd /4P if d the diameter of the mandrel and P the pressure in the pressure chamber. This pressure is between and kbar. The equipment is operative and permits satisfactory charging of the pressure chamber. However, the spacer tube takes up space in the pressure chamber which, among other things, is uneconomical.

Tubular pressure-generating punches have not so far been successful for pure hydrostatic extrusion, that is, extrusion without any axial force apart from the liquid pressure operating directly on the billet. Internal overpressure causes the punch to snap while external overpressure causes it to be compressed.

SUMMARY OF THE INVENTION The present invention is based on a press having a tubular pressure-generating punch and a rod passing through the punch which forms a mandrel or constitutes a holder for a mandrel.

The method according to the invention is characterised in that a hollow billet is shaped at one end with a smaller inner dimension than the outer dimension of the mandrel and is placed opposite the pressurechamber cylinder and die with the help of manipulating devices. The end having the smaller inner dimension is placed facing the die. The mandrel is than pushed into the billet. When the point of the mandrel reaches the part of the hollow in the billet which has a smaller dimension than the mandrel, the mandrel will press the billet against the die with a force dependent on the material and the size of the hole. In this way the billet can be kept in the desired position and in sealing contact with the die while the pressure chamber is closed and put under pressure.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described with reference to the accompanying drawings which show thepress at five stages during an extrusion cycle."

FIG. 1 shows the insertion of a billet opposite the die and the pressure-chamber cylinder,

'FIG. 2 the closing of the pressure chamber,

FIG. 3 a recently closed pressure chamber,

FIG. 4 the process just before extrusion is discontinued, and

FIG. 5 the opened pressure chamber after extrusion is complete.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawings 1 designates a horizontal press stand consisting of two yokes 2 and 3 connected to each other by a number of rods 4. A high-pressure cylinder 5 is axially movable in. the press stand and can be displaced by means of a number of operating cylinders, not shown. There is also an operating cylinder 6 in the stand, which is attached to the yoke 3. The operating cylinder is constructed of two concentric tubular parts 6a and 6b which form an annular space 7. In the operting cylinder is an annular piston 8. Pressure medium is supplied to the space 7 through a channel 9. The pressure-medium source is not shown. Return cylinders to move the piston 8 to the left to the positions shown in FIGS. 1, 2, 3 and 5 are not shown. The piston 8 is connected to a tubular pressure-generating punch 10. A rod 14 passes through the hole 11 in the yoke 3 and the hole 12 in the part 6b and the hole 13 in the punch 10, the front part of said rod forming a mandrel 14a and the part 14b forming a holder for the mandrel 14a. The mandrel holder 14b is connected to a piston 15 slidable in a cylinder 16 attached to the yoke 3. The spaces 17 and 18 on each side of the piston 15 are in communication with pressure-medium sources, not shown, through channels 119 and 20 provided with valves. Near the yoke 2 is a die 21. The yoke 2 constitutes the die support during an extrusion process. A billet is designated at 22. Seals 25 and 26 are provided in the high-pressure cylinder to seal between the cylinder 5 and the pressure-generating punch 10 and between the cylinder 5 and the die 21. The piston 8 is provided with seals 27 .and 28 to seal between itself and the cylinder sections 6a and 6b. The piston 15 is provided with seals 29 and 30 which seal between the piston and the cylinder 16. In the opening 11 in the yoke 3 is a seal 31 which seals between the yoke and the rod 14b. The mandrel 14a is provided with a seal 32 which seals between the mandrel and the pressure-generating punch 10. The billet 22 is provided at the front with a cone 33 which fits the inlet cone 34 of the die. The hole 35 in the billet 22 has a smaller diameter at the point 36 of the billet than the diameter of the mandrel 14a.

At the start of an operating cycle the parts of the press are in the positions shown in FIG. 1. With the help of manipulating devices, not shown, a billet 22 and a die 21 are applied between the yoke 2 and the cylinder 5 so that their center lines coincide with that of the high-pressure cylinder. The billet and the die are therefore placed opposite the hole 13 in the high-pressure cylinder 5. The space 17 in the operating cylinder 16 is supplied with pressure medium so that the piston 15 will displace the holder 14b and the mandrel 14a to the right. When the mandrel 14a reaches the point 36 of the billet, where the hole 35 has a smaller diameter than that of the mandrel, the mandrel 14a moves the billet towards the die 21 and then moves the billet and the die against the yoke 3 which acts as a die support.

The force with which the mandrel presses the billet against the die 21 and thus against the yoke 3 is primarily determined by the grip between the' billet and the mandrel at the point 36 of the billet. If the grip is suitably selected, the billet can be kept in the position shown in FIG. 2 and the manipulating devices removed. The cylinder 5 can than be pushed in over the billet and the die to the position shown in FIG. 3. The pressure chamber 40 is now completely closed and the billet abuts the mandrel 14a and the die 21. The pressure chamber 40 is filled with oil. In this position the seals 25 and 32 are in the same plane. The space 7 in the cylinder 6 is now supplied with pressure medium so that the piston 8 is displaced to the right and the pressuregenerating punch 10 is pressed into the pressure chamber 40, thus increasing the pressure therein. When the pressure has increased to a certain level, the extrusion starts. A tube 41 is formed in the gap between the man drel and the opening 42 in the die. When the units in the press are in the position shown in FIG. 4, the extrusion is discontinued. The piston 8 and punch 10 are returned to the left to their initial positions. The mandrel 14a is returned a little way to the left as shown in FIG. 5, after which the tube 42 is cut and the remnants 43 of the billet and the die 21 are removed. When the mandrel is drawn to the left to the position shown in FIG. I the billet remnants 43 are pressed against the end surface of the pressure-generating punch 10, the mandrel 14a is removed from the billet remnants and an operating cycle is conpleted and the next can be started.

I claim:

1. Method for hydrostatic extrusion of tubes in a press comprising a pressure chamber formed by a highpressure cylinder axially displaceable in a press stand, a die insertable into the cylinder and a tubular pressure-generating punch insertable into the cylinder to generate the pressure necessary for the extrusion process in a pressure medium enclosed in the pressure chamber and surrounding a billet to be extruded, a rod part passing through the pressure-generating punch, and a mandrel part carried by the rod part, which comprises placing a hollow billet shaped at one end with a smaller inner dimension than the outer dimension of the mandrel part in the press with the end of smaller inner dimension facing the die, pushing the mandrel part into the billet up to the point where the inner dimension is smaller than the outer dimension of the mandrel part, thereby pressing the billet against the die, and, while keeping the billet pressed against the die by the mandrel part, closing the pressure chamber and putting it under pressure to extrude the billet. 

1. Method for hydrostatic extrusion of tubes in a press comprising a pressure chamber formed by a high-pressure cylinder axially displaceable in a press stand, a die insertable into the cylinder and a tubular pressure-generating punch insertable into the cylinder to generate the pressure necessary for the extrusion process in a pressure medium enclosed in the pressure chamber and surrounding a billet to be extruded, a rod part passing through the pressure-generating punch, and a mandrel part carried by the rod part, which comprises placing a hollow billet shaped at one end with a smaller inner dimension than the outer dimension of the mandrel part in the press with the end of smaller inner dimension facing the die, pushing the mandrel part into the billet up to the point where the inner dimension is smaller than the outer dimension of the mandrel part, thereby pressing the billet against the die, and, while keeping the billet pressed against the die by the mandrel part, closing the pressure chamber and putting it under pressure to extrude the billet. 